1. Field of the Invention
The invention relates to electromagnetic apparatus for turning and/or lifting a slab of steel or other ferromagnetic material, and to a method of lifting and/or turning such a slab.
2. Description of Prior Art
Steel slabs are semi-finished products obtained in the steel industry by slab rolling or continuous casting. A slab may, for example, measure 12,000.times.2,000.times.225 mm, and weigh about 40 metric tons. The slabs are checked before further processing for inter alia surface flaws, such as tears. These flaws are removed by so-called "scarfing" with the aid of an oxygen burner. The slabs must be turned during checking and scarfing. By "turning" in this context is meant that the slab lying on the ground is turned with for example one of its longer sides used as the axis of turn, in such a way that the surface originally underneath comes to face upwardly. This is performed by means of an installation such as a crane (commonly a semi-gantry crane) equipped with a traversing trolley with an electromagnet. Known magnets used for this purpose are provided with a flat lifting surface.
A problem arising in turning a slab with a known magnet of this kind will be explained in the description with reference to the Figures. Briefly, contact between a slab and the electromagnet during turning is often interrupted, so that the slab falls to the ground. The booming sound that this produces is a nuisance not only to those working in the factory but also for nearby residents, particularly during the night. Another problem when turning a slab with the known kind of magnet is that jerking of the apparatus occurs, which leads to wear and other operative damage to the installation.
Several solutions of this problem are proposed in the prior art, but all involve the use of a plurality of magnets articulatedly connected to each other by bent arms. The magnets have flat faces to engage the slab and, by reason of their articulated connection, can engage both the opposite faces of the slab. See for example German Offenlegungsschrift Nos. 2,115,847 and 2,720,769 and U.K. Pat. Specification No. 1,421,762. Such an arrangement is excessively complex and difficult to put into practical operation.